First Look at the 2015 Lidar Data

As I mentioned in a previous post, we finished our final flights yesterday and are now in the process of demobilising, back in the Helistar hangar at Pochentong Air Base.

The data will take several weeks to fully process, but in the meantime our lidar engineers from McElhanney have been kind enough to provide us with some very rough, preliminary looks at the raw unprocessed data.

These shots below are simple cross-sections through central temple areas showing the laser returns that come from the ground (in pink) compared to the non-ground points from things like trees, grass and temple towers:

I’m not quite sure how many points we acquired in the 2015 lidar campaign but if the 2012 campaign is anything to go by, we should end up with something in the order of 40 billion individual point measurements after our 86 hours of acquisition flight time, although in theory (as we collected waveform data over Phnom Kulen) we could process many more discrete points out of the waveform data if we were interested in the finer details of tree structure. As archaeologists though we’re mostly interested in the ground returns, which reveal traces of ancient cities that have remained on the surface for a thousand years or more, which means processing the ground points into terrain models.

Again, courtesy of our lidar engineers at McElhanney, we’ve already gotten a first taste of what those terrain models look like, and although they are extremely rough and preliminary at this stage it’s still possible even at a glance to identify a whole bunch of previously-undocumented features at places like Banteay Chhmar and Sambor Prei Kuk:

To give you an idea of what we’re dealing with here, the image of Sambor Prei Kuk just above has been achieved through this kind of tree cover.

We’ll present more results here as they come online. In the meantime, sincere thanks are due to the hundred or so people who’ve worked day and night on making this project happen since the European Research Council announced funding for it only just in December. Purpose-designed archaeological lidar projects are different from other kinds of lidar acquisitions — which is why we’re flying in 40-something degree heat in the transitional period between the dry and wet seasons and destroying very expensive pieces of equipment! — and to give a sense of what’s been achieved, up until now the largest archaeological lidar campaign in history was in Belize in 2013, where they acquired about 1000 sq km. We’ve about doubled that in the last 4 weeks of flight ops, which even included 10 days of downtime due to equipment failure. Congratulations to all involved.

Disclaimer: All views and opinions expressed on this page are those of the author and do not necessarily represent official positions of APSARA, the EFEO or the Ministry of Culture and Fine Arts.